SUJET : Missing response data for a mandatory question

I have survey with approx 276 questions. All are "Array (Flexible Labels) dual scale" question type.
All questions are mandatory too. But in one participant's response, the first question's response data is missing. I'm wondering how the tool allows to skip the participant without answering the 1st question. Any knowledge base regarding this?

Hi Denis
Honestly I don't know about indexing. I checked the response in view response page as well as exported he data to xlsx. But in both that response is missing. Also the response status is "completed".

Hi, I am interested to know whether you resolved this issue as I am having the same problem. I have a survey with mostly mandatory questions (about 5 in 5 question groups). However, I have some responses marked as complete where only the last one or two question groups are showing data.